Classification of surface wind fields of tropical cyclones at landfall on the Japan main islands

A statistical study was made for surface wind fields of tropical cyclones (TCs) at landfall on the main islands of Japan using the AMeDAS data. The analysis was performed for 70 TCs which made landfall on the southern part (south of 36 degrees N) of the main islands during the period 1979-2004. The wind field within 200 km of each storm center was obtained by applying a composite analysis to hourly or ten-minute observations for the four hours around landfall, with the direction of storm motion as the y-axis. Then the fuzzy c-means method (FCM), which is a kind of cluster analysis, was applied to classify the wind distribution. All but one of the resulting five patterns show stronger winds on the right side of the center than on the left, with different degrees of right-left asymmetry and the shapes of the strong wind area. The five patterns have some differences in the preferred season, central pressure, speed and direction of motion, and regions of landfall of storms. A supplementary analysis using the wind profiler data, available from 2001, reveals that the right-left asymmetry is roughly explained by the storm motion, although the storm-relative wind fields still have some asymmetry.